Hi all, I'm new to the forum and a new pool owner. I purchased a 15x26 foot pool from the pool factory a month ago and had it installed by someone who was supposed to be a professional. The pool is 18 inches in the ground. Recently I saw two of the buttress slightly raising in the pool, you can see and feel it inside the pool. I called the pool installer who said this is normal. Is it normal, and will it affect the overall longevity? Thanks.